Pattern

ABSTRACT

The invention relates to a pattern ( 18 ) which is designed as a visually perceptive mosaic consisting of a plurality of surface elements ( 8; 9; 15; 16; 17 ) and which is embedded in a laminate ( 1 ) consisting of at least one transparent outer layer ( 2 ) and one protective layer ( 5 ). The surface elements ( 8; 9; 15; 16; 17 ) are transparent, scatter or reflect incident light ( 10 ) or diffract the incident light ( 10 ) to microscopic relief structures covered with a reflecting layer ( 3 ). An area ( 16 ) corresponding to at least one of the surface elements provided with a microscopic relief structure ( 4 ) has a ZOM structure ( 4′ ) with a profile height h which can be slowly modified in a pre-determined manner and a spatial frequency f. The product of a predetermined critical wavelength λ G  of the visible spectrum and the spatial frequency f is greater than or equal to  1.

[0001] The invention relates to a surface pattern of the kind set forthin the classifying portions of claims 1-11.

[0002] Such surface patterns have a microscopically fine reliefstructure and are suitable as security elements for enhancing the levelof security against forgery of value-bearing papers or securities andbonds, passes, payment means and other valuable articles.

[0003] A surface pattern of the kind set forth in the classifyingportion of claim 1 is known from WO 87/07034. The surface pattern hasthree surface portions with an optically effective diffractionstructure. Those structures with a spatial frequency f diffract visiblelight according to its wavelength λ at different diffraction angles α.The profile height h of the grooves of the three structures is constantin each surface portion, but it is established differently in eachsurface portion in such a way that, for a given observer, the firststructure diffracts blue light, the second structure green light and thethird structure red light, with in each case a vanishing or minimumlevel of diffraction efficiency. When the surface pattern is tiltedabout an axis which is parallel to the grooves of the structures, thefirst surface portion will appear dark at a first viewing angle, thesecond surface portion will appear dark at a second viewing angle andthe third surface portion will appear dark at a third viewing angle,that is to say from the point of view of the observer the dark surfaceportion abruptly changes in position as the surface pattern iscontinuously tilted. The spatial frequency f is limited upwardly as theoptical effect described here is observable in the first diffractionorder.

[0004] WO 98/26373 describes a surface pattern with diffraction gratingswith a light-dark pattern, the extent of which changes with the viewingangle. The profile heights h of the gratings change in accordance with amodulation function. The spatial frequencies f are so selected that atleast a first diffraction order occurs.

[0005] EP 0 712 012 A1 describes a surface pattern which includes anelement with a diffraction structure coated with a lacquer, with aspatial frequency f of more than 2000 lines/mm. It is pointed out that,for such spatial frequencies, because of total reflection at thelacquer-air-interface, visible light diffracted at the diffractionstructure, even in the first diffraction order, remains trapped in thelacquer layer. The diffraction structure is produced through a mask bymeans of an anisotropic etching process. The profile heights h depend onthe size of the openings in the mask or the duty ratio of thetransparent and opaque surfaces and are only statistically establishedby virtue of the etching process. Because of imponderables in theetching process a predetermined pattern cannot be precisely convertedinto the diffraction structure. A holographic copy of the diffractionstructure has a similar diffraction performance to the originalwhich—because it is itself imprecisely defined—scarcely differs from thecopy, from the point of view of a lay person.

[0006] On the other hand EP 0 105 099 B1, EP 0 330 738 B1 and EP 0 375833 B1 disclose surface patterns with surface portions which areassembled in a mosaic, with various diffraction structures which arevisible in dependence on the tilt angle and/or angle of rotation andwhich show a sequence of patterns or images. The surface patterns whichhave an optical diffraction effect are embedded between layers oftransparent plastic materials (Swiss patent specification No 678 835).

[0007] The object of the present invention is to provide a forgery-proofand copying-proof diffraction structure which by virtue of a highspatial frequency has a clearly recognisable pattern.

[0008] That object is attained with the characterising features ofclaims 1-11. Advantageous configurations are set forth in the appendantclaims.

[0009] Embodiments of the invention are described in greater detailhereinafter by way of example with reference to the drawing in which:

[0010]FIG. 1 is a view in cross-section of a laminate,

[0011]FIG. 2 is a diagrammatically sub-divided surface pattern,

[0012]FIG. 3 shows the simple surface pattern,

[0013]FIG. 4 shows a profile of a relief structure,

[0014]FIG. 5 shows the profile with another envelope curve,

[0015]FIG. 6 shows the profile with the envelope curve with a constantterm K,

[0016]FIG. 7 shows the profile in the region of small profile heights,

[0017]FIG. 8a shows an area in the region of small profile heights,

[0018]FIG. 8b shows the area from a different viewing direction,

[0019]FIG. 9 shows envelope curves,

[0020]FIG. 10 shows the envelope curve surface for a chessboard pattern,

[0021]FIG. 11 shows symmetrical and asymmetrical profiles, and

[0022]FIG. 12 shows a profile shape which changes along a direction.

[0023] In FIG. 1 reference 1 denotes a laminate, 2 denotes a transparentcover layer comprising a polymer, 3 denotes a reflection layer, 4denotes a microscopic relief structure, 5 denotes a protective layercomprising a polymer and 6 denotes a substrate. The surface of theprotective layer 5, which is remote from the reflection layer 3, iseither covered with an adhesive layer 7 or the protective layer itselfperformas the function of the adhesive. Cold or hot melt adhesives aresuitable as the adhesive, the choice depends on the use involved. Themicroscopic relief structure 4 is formed into the cover layer 2 andcovered with the reflection layer 3 while the unstructured surfaceportions 8 and 9 are covered, as mirror surfaces 8, with the reflectionlayer 3, or, as transparent windows 9, remain free of the reflectionlayer 3. Either the protective layer 5 is recognisable through thewindows 9 or, if the protective layer 5 is also transparent, indicia ofthe substrate 6 are visible under the laminate 1.

[0024] The microscopic relief structure 4 is an optically effectivegrating with parallel straight or curved grooves and at least locallyinvolves a periodic structure which is described by the parametersthereof. The most important parameters are an azimuth angle relative toa particular direction, a spatial frequency f or a number of grooves permillimetre, a relief profile shape, and a profile height h. Thegeometrical profile height h_(G) within the microscopic relief structure4 is not to be confused with the optically effective profile height h.If the material of the cover layer 2 of the refractive index n fills thegrooves of the relief structure 4, the geometrical profile height h_(G)multiplied by the refractive index n becomes optically effective as theprofile height h. Hereinafter the profile height h always means theoptically effective profile height h.

[0025] The wavelengths perceived by the human, eye cover a range of 380nm (violet) to 780 nm (red).

[0026] A light beam 10 which is incident on the microscopic reliefstructure 4 at an angle α on the laminate 1 is partially reflected anddiffracted at the reflection layer 3. As the cover layer 2 has a typicalrefractive index of n=1.5, the incident light beam 10 is refracted inrelation to a perpendicular 11 on to the surface of the cover layer 2before it impinges on the microscopic relief structure 4 and isdiffracted. The diffracted light 12 leaves the microscopic reliefstructure 4, in accordance with the diffraction order, with thereflected light beam 4 leaving the laminate 1 in the zero diffractionorder, in the direction 13 of the reflected light. The other diffractionorders include additional angles β relative to the reflected light beam14, wherein those additional angles β are given by the function sinβ=m·λ·f+sin (β_(IN)), provided that m denotes the number of thediffraction order, λ denotes the wavelength of the incident light beam10 and f denotes the spatial frequency of the relief structure 4. ASsoon as the diffracted light 12 impinges on the interface of the coverlayer 2 relative to the air at an angle γ of more than arcsin (1/n), thediffracted light 12 is totally reflected and issues from the laminate 1only after a plurality of reflections, in directions which can no longerbe defined. However as soon as the product of a limit wavelength λ_(G)and the spatial frequency f is greater than or equal to 1, no morediffraction occurs. The limit wavelength λ_(G) depends on the lightsource provided for observation. If observation under daylightconditions is involved, the limit wavelength λ_(G) is advantageouslyselected to be in the violet part of the visible spectrum, for exampleλ_(G)=380 nm. That determines the minimum spatial frequency f as 2′630per mm.

[0027] In contrast light is very well reflected at the reflection layer3, in which respect differences in height within the microscopic reliefstructure 4 cause path length differences and thus phase differencesbetween the light beams 14 reflected at adjacent points. Interferencebetween the reflected light beams 14 with the phase differencesinfluences the intensity of the light in dependence on the wavelength λ.Therefore, from that white light, the light of given wavelengths λ areamplified, reduced or even extinguished. The microscopic reliefstructure 4 in which there is no longer any diffraction but only theeffect of interference can still be observed in the zero diffractionorder is referred to as a ‘zero order microstructure’ or ZOM.Hereinafter the microscopic relief structures 4 which satisfy thecondition λ·f≧1 are referred to as ZOM-structures 4′. A surface which isoccupied by the ZOM-structure 4′ and involves a profile height h whichis constant over the surface, appears in the grey value or colourdetermined by the profile height h and the material of the reflectionlayer 3, upon illumination of the laminate 1 with white light in a lightbeam 10 incident from one direction. When the surface is tilted about anaxis in the plane of the surface in contrast the optically effectiveprofile height h changes and therewith the colour, the colour shade orthe grey value. In the case of normal diffuse illumination the incidentlight 10 is incident on the microscopic relief structure 4 over theentire half-space over the laminate 1 and leaves the laminate in thesame distribution into the half-space. In the case of selectedZOM-structures 4′ an observer sees the surface in a colour which isdependent on the tilt angle but not the azimuth. The ZOM-structures 4′with a rectangular profile stand out due to rich colours and are alsoknown from nature, an example in this respect is the coloured wings ofbutterflies of the Morphus family.

[0028] The ZOM structure 4′ has a line spacing 1/f which is less thanthe wavelength λ of the visible light. Scalar theory cannot evenqualitatively describe the diffraction behaviour of the ZOM-structure4′, only an application of the exact electromagnetic theory and precisecalculations as are described in the book ‘Electromagnetic Theory ofGratings’ by R Petit, editor, Springerverlag, Heidelberg 1980. Inaccordance therewith scalar theory fails because the behaviour of lightis completely different in accordance with TE-and TM-polarisation.

[0029] In the case of TE-polarisation in which the electrical field isoriented parallel to the grooves of the ZOM-structure 4′ surfacecurrents flow in the (continued from line 10 of page 6 of thetranslation of the PCT text) advance into the depth of the ZOM-structureand is only there reflected. The result is that, in the region of theprofile height h of 0 to about 350 nm, the reflectivity of theZOM-structure 4′ in metal decreases substantially with increasingprofile height h.

[0030] In contrast to the usual diffraction structures with thecondition λ·<1 the colour of the ZOM-structures 4′, which can beperceived under a given observation condition, has not been derived fromthe diffraction equations. The colour of the ZOM-structures 4′ dependson the materials, the profile shape, the profile height h, theorientation and so forth and is generally not a spectral colour. Whenusing metallic reflection layers 3, grey or metallic colour shadesappear upon illumination of the ZOM-structures 4′ with white light. Withcrossed gratings, the formation of surface currents can be suppressed,in which case the ZOM-structures 4′ reflect only still a little light.Such a ZOM-structure 4′ with a metallic reflection layer 3 appears blackfrom all angles of view. Dielectric reflection layers 3 behavedifferently. Upon rotation about the perpendicular 11 the ZOM-structure4′ with the dielectric reflection layer 3 exhibits colour shadingeffects or colour changes which are dependent on the azimuth.

[0031] The advantage of those ZOM-structures 4′ with λ·f≧1 is that theobserver always sees a coloured or grey-shaded surface, irrespective ofthe observation conditions, quite in contrast to a mosaic consisting ofsurface portions with the known diffraction gratings, as are describedin above-mentioned documents EP 0 105 099 B1, EP 0 330 738 B1and EP 0375 833 B1.

[0032] If the microscopic relief structure 4 does not have a periodicstructure but is of dimensions which are greater than the wavelength λof the incident light, no diffraction occurs; however the light isscattered. By means of a suitable profile shape the light is scatteredin a preferred direction. A scattering surface portion without apreferred direction appears to the observer as a grey surface,independently of the azimuth; a scattering surface portion with apreferred direction is perceived as a light or a dark surface, dependingon the observation direction. (continue at line 11 of page 7 of thetranslation of the original PCT text) (continued from line 12 of page 8of the translation of the original PCT text) modulated with a functionH(z). The profile height h changes within the area 16 (FIG. 3) along aparticular direction z, for example with a linear function H(z). Theparticular direction z is oriented for example parallel to the gratingvector of the grating structure G(z). An envelope curve 22, that is tosay the function H(z), is for example of a periodic sawtooth shape andis composed of a plurality of linear portions, wherein the function Hassumes values of the profile height h between h=0 nm and a maximum. TheZOM-structure 4′ thus has the profile 21 of the function S(z)=G(z)·H(z).A special case of that function is given if the function, in an area 16,only assumes the values of a single period on the path z between an edgeportion of the area 16 to an oppositely disposed edge portion of thearea 16.

[0033]FIG. 5 shows another profile 21 of the ZOM-structure 4′ (FIG. 1)in which the sinusoidal grating structure G(z)=0.5·A·[1+sin(2πfz)] ismodulated with the envelope curve 22 of the function H(z)=sin²(2πFz),wherein F is the frequency of the envelope curve 22. The profile 21assumes the values of the function S(z)=0.5·A·[1 +sin(2πfz)]πsin²(2πFz).

[0034]FIG. 6 shows a function H(z) of the profile height h, which has aconstant additive term K. The Figure shows the envelope curve 22 of thefunction H(z)=sin²(2πFz)+200 nm. The profile 21 of the ZOM-structure 4′(FIG. 1) only attains the minimum profile height K=200 nm in the area 16(FIG. 3). That minimum profile height K is selected from the range0<K<300 nm. Any conceivable function suitable for modulation of thegrating structure G(z) may have such an additive term K. The minimumprofile height K in the region of at least 50 nm and better 100 nm to200 nm prevents the occurrence of locations without an adequate profile.The locations without an adequate profile reflect the entire spectrum ofthe incident light. The area 16 with such a ZOM-structure 4′ has regionsof different colours which correspond to the different interferenceconditions. In the regions with the profile height h=K for example theblue components are missing while with an increasing profile height hlight of a longer and longer wavelength is faded out, for example greenat h≈250 nm to 300 nm, so that an observer sees a purple colour.

[0035] In general terms, for good observability of the surface pattern18 (see FIG. 2), a slow change in the profile height h in the particulardirection z is necessary, that is to say, the frequency F is to beselected to be much less than the spatial frequency f, while desirablythe spatial frequency f is to be selected as greater than f=2400periods/mm and the frequency F is to be selected from the range F<5periods/mm. In the drawings in FIGS. 5 to 7 with the profiles 21 and theenvelope curves 22 a period of the envelope curve 22, for reasons ofillustration in the drawings, includes only a few periods of the profile21 of the ZOM-structure 4′. In these examples the profile height h isspecified in micrometers and the distances in the direction z inmillimetres. In reality therefore the spatial frequency f of the profile21 is a multiple higher than the frequency F of the envelope curve 22,that is to say the profile height h changes very slowly in dependence onthe locus (x, y) except for individual non-uniformities. In the area 16(FIG. 2) with the ZOM-structure 4′, which is illuminated with daylight,the observer perceives a colour or grey value which is adjustedaccording to the local value of the envelope curve 22. The periodicityof the envelope curve 22 thus produces a periodic pattern with thefrequency F. So that the pattern can be readily perceived without aid,the period of the envelope curve 22 extends at least over 0.2 mm. Asingle period of the envelope curve 22 contains for each millimetrealong a distance in the particular direction z the number of periods ofthe profile 21, which is specified by the spatial frequency f.

[0036] As stated above the ZOM-structures 4′ have a strong polarisingaction. When viewing the ZOM-structure 4′ in polarised light or whenviewing through a polarisation filter 31 (FIG. 1) and with illuminationin unpolarised light the pattern produced by the changing profileheights and/or profile shapes, in the area 16, is visible in an enhancedcontrast or pronounced colours when the reflected TE-component of thelight is eliminated by rotation of the polarisation filter 31. Forexample area portions 32 (FIG. 2) within the area 16 have suchZOM-structures (4′) which differ from the ZOM-structure (4′) of theremaining area 16 serving as a background surface, only by virtue of adifferent polarisation capability. If the area portions 32 form aninformation-bearing code, for example in the form of a bar code, thecode is not visible in light 10 (FIG. 1) which is incident innon-polarised mode as there is no contrast between the area portions 32and the background surface of the area 16. It is only upon illuminationwith polarised light 10 that sufficient contrast occurs to (continue atline 18 of page 10 of the translation of the original PCT text) (FIG.1). It extends perpendicularly to the particular direction z, as isshown in a plan view on to the area 16 in FIGS. 8a and 8 b. The area 16with a part of its border 19 adjoins another surface portion, forexample the optical-diffraction surface 15. If the observer in FIG. 8ais looking substantially perpendicularly on to the plane of the drawingin the observation direction 23 on to the ZOM-structure 4′ (FIG. 1),over a distance of z=0 to z=z₁, the profile height h given by theenvelope curve 22 (FIG. 7) is too small for the TM-polarised light to benoticeably weakened. In FIG. 8a therefore a sub-area 24 and anintermediate area 24′ of the area 16 act like a mirror while a region 25of the area 16 has profile heights h which are sufficiently great forinterference colours and the area 25, as stated above, appears in colouror in a grey shade or a mixed colour. This is indicated in the drawingin FIGS. 8a and 8 b by a dot raster. The profile height h in the region25, at the boundary 26 to the intermediate area 24′, reaches at least 80to 100 nm, that is to say there for example the blue components arecancelled out of the white light. If the observer tilts the surfacepattern 18 (FIG. 2) with the ZOM-structure 4′ (FIG. 1) about an axisparallel to the grooves of the profile 21 (FIG. 7) into an inclinedposition, he notices that the region 25 expands at the cost of theintermediate area 24′, the transition between the mirror and theinterference colours shifts from the boundary 26 of z=z₁ to z=z₂ to thedotted line 26′, and reaches for example the sub-area 24. The observeris now looking inclinedly in a viewing direction 27 on to the profile21. In FIG. 7 that causes an increase in the size of the profile heighth to the effective profile height h_(w) so that these interferenceeffects also already occur at z=z₂ in the intermediate area 24′ (FIG.8b). The model of the profile height h, which is shown here, is only aheuristic one; the model cannot correctly reproduce the truecircumstances in relation to sub-microstructures.

[0037] The above-described example is illustrated in FIGS. 8a and 8 b.In the intermediate area 24′ the profile height h of the ZOM-structure4′ rises from at most 50 nm at the line 26′ to at least 80 nm to 100 nmat the boundary 26 to the region 25. In the reflective sub-area 24 theprofile (continued from line 27 of page 12 of the translation of theoriginal PCT text) portions 24, 24′ in order easily to recognise thedisplacement of the boundary 26 in the direction of the dotted line 26′.The marking surface 26′ is occupied by diffracting, absorbing orscattering structures which for example light up or are readily visiblewhen in the intermediate area 24′ the transition from specular tocoloured reflection is at the boundary 26 and/or at the location of thedotted line 26′.

[0038] Not only the sine function used above as an example but alsoother trigonometric functions such as sin^(b)(2πfz) with b=2, 3, 4, 5, .. . or other periodic functions such as cycloids, rectangular functionsor triangular functions, are suitable for the grating structure G(z).The cross gratings formed from those functions are to be particularlymentioned. Particularly for deep structures a function sin^(b(z))(2πfz)is suitable, in which b(z) is a function which is steady in aportion-wise manner.

[0039] The modulating envelope curve 22 of the profile 21 determines theobservable patterns in the area 16. Besides the above-describedfunctions it is also possible to use the straight trigonometricfunctions sin^(b)(2πfz) with b=2,4,. . . and those shown in FIGS. 9a to9 d. FIG. 9a shows the function H(z)=|sin(2πFz)|, FIGS. 9b and 9 c showlinear periodic functions H(z) and FIG. 9d shows a non-periodicparabolic function H(z). The profile heights h are randomly selected andtherefore the ordinate in FIGS. 9 is not scaled.

[0040] The profiles 21 and the envelope curves 22 extend perpendicularlyto the plane of the drawing in FIGS. 4 to 7 and 9 between the borders 19of the area 16.

[0041] In quite general terms the profile 21 of the ZOM-structures 4′,S(x, y), is produced by modulation of the high-frequency gratingstructure G(x, y) with a modulating function H(x, y) of the profileheight, which changes over several 1000 periods of the grating structureG(x, y) between a minimum and a maximum value: S(x, y)=G(x, y)·H(x, y),wherein the coordinates x and y identify a location in the area 16.

[0042] By way of example FIG. 10 shows an envelope curve surface 28which in terms of its shape reminds us of an egg carton. The envelopecurve surface 28 contains all envelope curves 22 in the area 16 anddetermines the profile height h at each location which is established bythe co-ordinates x, y. The identified envelope curve 22 has the functionH(x, y (continue at line 30 of page 13 of the translation of theoriginal PCT text) so that the ZOM-structure 4′ (FIG. 1) has thefunction

S(x,y)=0.5·A·[1+sin(2πfx)]·[1+sin(2πfy)]·sin(2πFx)·sin(2πFy)+K.

[0043] That ZOM-structure 4′ comprises fine, regularly arranged needleswhose length is determined by the envelope curve surface 28. Underdiffuse illumination a chessboard-like molrépattern becomes visible, inwhich respect hills 29 stand out from valleys 30 in respect of colourand/or in the grey values. In this case also the colours and grey valueschange when the area 16 is tilted but not when the area 16 is rotatedabout the perpendicular line 11. If the term K<50 nm the bottoms of thevalleys 30 reflect. The shift of the transition from specular tocoloured reflection when the area 16 is tilted is also to be observed inthe region of the inclines of the envelope curve surface 28 in thechessboard-like moirépattern.

[0044] In another embodiment the ZOM-structure 4′ has a relief with theprofile 21 (FIG. 4) in accordance with the function S(x, y), whereinS(x, y) is an additive superimposition of two periodic functions G1(x,y) and G2(x, y), The function G1(x, y) is sinusoidal, is of theamplitude A and determines the spatial frequency f of the ZOM-structure4′. The second function G2(x, y, θ) is the first harmonic in relation toG1(x, y) and is of the amplitude A/2. The function G2(x, y, θ) isdisplaced by a phase θ with respect to the function G1(x, y). In thegeneral form

S(x, y)=G1(x, y) +G2(x, y).

[0045] In the particular direction z the function S of the ZOM-structure4′ reads:

S(z)=A·{[1+sin(2πfz)]+0.5·[1+sin(4πfz+θ)]}.

[0046]FIGS. 11a to lid and 12 show the profile 21 (FIG. 7) as a functionalong the direction z, wherein the ordinate h is scaled in arbitraryunits. The value of the phase shift θ determines whether theZOM-structure 4′ is symmetrical, as shown in Figs. 11b and lid (forθ=90° and 270° respectively) or asymmetrical, as shown in FIGS. 11a and11 c (for θ=0° or 180° respectively). The grating vectors of thefunctions G1(x, y) and G2(x, y) are parallel or include an angle with anabsolute magnitude of less than 10°. (continued from line 32 of page 14of the translation of the original PCT text)

[0047] In another embodiment of the ZOM-structure 4′ the phase shift θis a periodic or at least a portion-wise steady function θ(x, y) of thelocation in the area 16 (FIG. 10). The function θ(x, y) changes veryslowly in comparison with the spatial frequency f in the direction z,for example in the range of 90°/mm to 720°/mm. The function θ(x, y)modulates the profile shape of the ZOM-structure 4′ and thus has aneffect comparable to the function of the envelope curve 22 (FIG. 5).FIG. 12 shows a local variation in the curve shape of the ZOM-structure4′ as a function of the particular direction z. In the case of theperiodic function θ (x, y) the phase shift θchanges through 360° over anumber of N periods of the ZOMstructure 4′ with the spatial frequency f.The pattern which occurs upon illumination of the ZOM-structure 4′ isthus repeated at spacings of N/f mm.

[0048] The range of profile heights h which can be achieved forZOM-structures 4′ depends on the spatial frequency f as an inexpensivemultiplication, that is to say replication of the ZOM-structure 4′ inthe cover layer 2 (FIG. 1), becomes correspondingly more difficult, thehigher the spatial frequency f is. The profile heights which can beproduced nowadays are in the range of h=0.5/f to 4/f. With a spatialfrequency of f=3000 periods/mm the profile heights h are in the range of150 nm to 1200 nm. Typical values for the profile heights h are between200 nm and 400 nm at a spatial frequency f of 3000 periods/nm.

[0049] The observation condition for the observer changes if the surfacepattern 18 (FIG. 2) is tilted about an axis in the plane of the surfacepattern 18 or is rotated about the perpendicular line 11 (FIG. 1).Likewise the quality of the incident light, colour, polarisation and soforth or viewing of the surface pattern 18 through a polarisation filter31 (FIG. 1) and rotation of the polarisation filter 31 influence theobservation condition.

1. A surface pattern (18) with a visually visible mosaic comprising anumber of surface portions (8; 9; 15; 16; 17) embedded in a laminate (1)of at least a transparent cover layer (2) and a protective layer (5),wherein the one surface portions are in the form of transparent windows(9) and the other surface portions (8; 15; 16; 17) which are at leastpartially covered with a reflection layer (3) are in the form of mirrorsurfaces (8), optical-diffraction surfaces (15, 16) with microscopicrelief structures (4; 4′) and surface portions (17) which scatterincident light beams (10), characterised in that for a predeterminedlimit wavelength (λ_(G)) of the visible spectrum at least in one of theoptical-diffraction surfaces (15; 16) in an area (16) defined byco-ordinates x and y the microscopic relief structure is in the form ofa ZOM-structure (4′) and is of a spatial frequency (f) such that theproduct (P) of the limit wavelength (λ_(G)) and the spatial frequency(f) is greater than or equal to 1, in the other optical-diffractionsurfaces (15) the spatial frequencies (f) of the other microscopicrelief structures (4) satisfy the condition that the product (P) is lessthan 1, and in each location defined by the co-ordinates (x, y) in thearea (16) a profile height (h) of the ZOM-structure (4′) is opticallyeffective, wherein a grating structure (G{x, y}) of the ZOM-structure(4′) is modulated by means of a low-frequency envelope curve surface(28; H{x, y}) at a frequency (F), wherein the frequency (F) is less thanfive periods per millimetre.
 2. A surface pattern (18) according toclaim 1 characterised in that the envelope curve surface (28; H{x, y})determines values for the profile height (h) from the range 0 nm to amaximum value which is between 150 nm and 1200 nm and that the area (16)with the ZOM-structure (4′) has reflecting sub-areas (24; 24′).
 3. Asurface pattern (18) according to claim 1 characterised in that theenvelope curve surface (28; H{x, y}) has values for the profile height(h) an additional constant term with a value K from the range of 50 nmto 200 nm, that the envelope curve surface (28; H{x, y}) assumes valuesfor the profile height (h) from the range K to a maximum value which ishigher than 150 nm but less than 1200 nm, and that the area (16) withthe ZOM-structure (4′) does not have any reflecting sub-areas (24; 24′).4. A surface pattern (18) according to claim 2 or claim 3 characterisedin that the envelope curve surface (28; H{x, y}) is a periodictrigonometric function.
 5. A surface pattern (18) according to one ofclaims 1 to 4 characterised in that the envelope curve surface (28; H{x,y}) is a periodic function composed of linear portions.
 6. A surfacepatter (18) according to one of claims 1 to 5 characterised in that thetwo-dimensional envelope curve surface (28; H{x, y}) along a particulardirection (z) is a one-dimensional function (H{z}) such that the area(16) has a strip-shaped colour and/or grey value pattern in thereflected light (14).
 7. A surface pattern (18) according to one ofclaims 1 to 5 characterised in that the two-dimensional envelope curvesurface (28; H{x, y}) is a product of the sub-function (H1) whichchanges only in the direction of the one co-ordinate (x) and thesub-function (H2) which changes only in the direction of the otherco-ordinate (y) such that the area (16) has a chessboard-like regularcolour and/or grey value pattern in the reflected light (14).
 8. Asurface pattern (18) according to claim 6 or claim 7 characterised inthat the dimensions of the colour and/or grey values of the pattern aredependent on the observation conditions and are variable by tiltingabout an axis in the plane of the area (16).
 9. A surface pattern (18)according to one of claims 1 to 8 characterised in that a period of theenvelope curve surface (28; H{x, y}) includes a number of M periods ofthe ZOM-structure (4′) with the spatial frequency (f) and that thepattern is repeated at a spacing of M/f mm.
 10. A surface pattern (18)according to one of the preceding claims characterised in that thegrating structure (G{x,y}) is proportional to the functionsin^(b(z))(2πfz), wherein b(z) is at least a portion-wise steadyfunction in a particular direction (z) in the area (16) defined by theco-ordinates (x;y).
 11. A surface pattern (18) with a visually visiblemosaic comprising a number of surface portions (8; 9; 15; 16; 17)embedded in a laminate (1) of at least a transparent cover layer (2) anda protective layer (5), wherein the one surface portions are in the formof transparent windows (9) and the other surface portions (8, 15; 16;17) which are at least partially covered with a reflection layer (3) arein the form of mirror surfaces (8), optical-diffraction surfaces (15,16) with microscopic relief structures (4; 4′) and surface portions (17)which scatter incident light beams (10), characterised in that for apredetermined limit wavelength (λ_(G)) of the visible spectrum at leastin one of the optical-diffraction surfaces (15; 16) in an area (16)defined by co-ordinates x and y the microscopic relief structure is inthe form of a ZOM-structure (4′) and is of a spatial frequency (f) suchthat the product (P) of the limit wavelength (λ_(G)) and the spatialfrequency (f) is greater than or equal to 1, in the otheroptical-diffraction surfaces (15) the spatial frequencies (f) of theother microscopic relief structres (4) satisfy the condition P=λ_(G)·fis less than 1, and in each location defined by the co-ordinates (x, y)in the area (16) a profile height (h) of the ZOM-structure (4′) isoptically effective, the ZOM-structure (4′) is an additivesuperimposition of a first periodic function (G1) and a second periodicfunction (G2), wherein the first function (G1) of an amplitude (A)determines the spatial frequency (f) of the ZOM-structure (4′) and thesecond function (G) is the first harmonic in relation to the firstfunction (G1) of half the amplitude (A) and wherein the second function(G2) is displace by a phase (θ) with respect to the first function (G1),and that both the two functions (G1; G2) and also the phase (θ) arefunctions which are dependent on the co-ordinates (x;y).
 12. A surfacepattern (18) according to claim 11 characterised in that the phase (θ)is a periodic function (θ), that a period of the phase (θ) includes anumber of N periods of the ZOM-structure (4′) with the spatial frequency(f) and that the relief of the ZOM-structure (4′) is repeated at aspacing of N/f mm.
 13. A surface pattern (18) according to claim 11characterised in that the phase (θ) changes along a particular direction(z) in the area (16) defined by the co-ordinates (x,y) at a speed of 90°per millimetre to 720° per millimetre.
 14. A surface pattern (18)according to claim 11 characterised in that the grating vectors of thetwo functions (G1, G2) include an angle of an absolute magnitude of lessthan 10°.
 15. A surface pattern (18) according to one of the precedingclaims characterised in that the predetermined limit wavelength λ_(G) isthe shortest wavelength λ which is still just visible.
 16. A surfacepattern (18) according to one of the preceding claims characterised inthat an area (16) with a ZOM-structure (4′) has along a distance acommon border (19) with one of the other surface portions (15) having anoptical-diffraction effect.
 17. A surface pattern (18) according to oneof the preceding claims characterised in that area portions (32) in thearea (16) form information and that the ZOM-structures (4′) of the areaportions (32) differ from the ZOM-structure (4′) of the rest of the area(16) only by a differing polarisation capability for the incident lightbeams (10).
 18. A surface pattern (18) according to one of the precedingclaims characterised in that a marking surface (26″) which diffracts orscatters the incident light beams (10) is arranged adjoining the area(16) so that in a predetermined observation direction (23) the markingsurface (26″) identifies the location of a limit at which in a colourand/or grey value pattern of the ZOM-structure (4′) specular reflectionchanges to coloured reflection and that with other observationconditions the transition from specular to coloured reflection isdisplaced with respect to the marking surface (26″).